The present invention relates in general to semiconductor technology, and more specifically, to a circuit for facilitating operation of Complementary Metal-Oxide Semiconductor (CMOS) devices, such as CMOS switches.
To control a CMOS analog switch, such as a switched capacitor (SC) circuit, two complementary control signals are typically employed. These control signals are able to fully open or close the two complementary MOSFETs of the SC circuit. For control levels, the two supply voltages VDD and VSS of an integrated circuit are normally used. Disadvantageously, the trend towards ever smaller operating voltages drastically reduces the effective control voltage available to open the MOSFETs of an SC circuit. A critical case arises if the signal voltage is approximately VDD/2. At this condition, the effective control voltage to the N-MOSFET of the SC circuit would be:VCN=−VDD−VTHN−VDD/2=VDD/2−VTHN and the effective control voltage to the P-MOSFET of the SC circuit would be:VCP=−VDD/2−VTHP. 
Considering that the amount of the two threshold voltages is further increased by the body-effect and taking into account technological dispersions, the effective control voltage at supply voltages as small as 2.4 volts almost becomes zero, and thus, proper working of an SC circuit with small operating voltages (e.g., 1.8 V) would not be possible.